[wadeekha]

1. ) 10cm^3 of a hydrocarbon CxHy were exploded in an excess of oxygen. There was a contraction in volume of 30cm^3. When products were treated with sodium hydroxide ( which reacts with carbon dioxide ), there was a further contraction of 30cm^3. Deduce the formula of the hydrocarbon, given that all volumes were measured under the same conditions.

2. ) 10g of a hydrocarbon of Mr= 800 completely reacted with 1.8dm^3 of hydrogen measured at room temperature and pressure. Calculate the number of moles of hydrogen that react with one mole of hydrocarbon. Hence, deduce how many C=C bonds there are in one molecule of this oil.

I got the answer for the number of moles of hydrogen that react with 1 mole of hydrocarbon.
10g/800 = 0.0125 mol of hydrocarbon
1.8 dm^3/ 24 = 0.075 mol of hydrogen
1/ 0.0125 mol = 80
0.075 mol x 80 = 6
Thus 1 mol of hydrocarbon will react with 6 moles of hydrogen.
However for the number of C=C bonds, the answer is 6 and I have no idea how to arrive at that answer.
Questions that occurred during my revision.
3.) Are diastereomers and emantiomers of a substance under the same homologous series?
4. ) Is thermal cracking = combustion?


Thank you soo much for your time!

[cth]

1)  To help you get started, writing chemical reactions is always a good idea (I let you work out stoechimetric coefficients):

C_xH_y + ?? O₂  ?? CO₂ + ?? H₂O

Once you have done this, you can use ideal gas state equation: PV=nRT  (where P is pressure, V is volume, n is mole number, R is the ideal gas constant and T is temperature).
After working up your equations, you should end up with something like this: y = ax + b.
Then, you can deduce the hydrocarbon formula.

2)  You're almost done there. All you need to do is write down the chemical reaction and see how many moles of H₂ reacts with one mole of C=C

R   R                 R  R
|    |                  |  |
C=C + H₂  R-C-C-R
|    |                  |  |
R   R                 H  H

3) and 4), definitions can be found on Wikipedia



Hope it helps